Keeping cool, using a Raspberry PI to create a networked temperature sensor Keeping cool By Dwight Hubbard dwight@dwighthubbard.com Using a Raspberry PI to create a networked temperature sensor

How this got started We wanted to ensure our cat was safe during our pit stops on road trips.

Next Up Choosing the Hardware

Raspberry Pi Hardware Connections The Raspberry Pi has a General Purpose Input Output (GPIO) pins that can be used to connect to electronics. These pins allow connecting electronics directly to the system. This is really powerful

Raspberry Pi GPIO requirements When choosing electronics to connect to the Raspberry PI GPIO pins there are 2 simple rules: ☐ Component must operate at 3.3 volts ☐ Component must be digital

The Temp Sensor Maxim/Dallas DS18B20 Operates at 3.3 Volts ○ Supports 3.0Volts to 5.5Volts Digital ○ Uses a serial (digital) protocol Driver - Built into the Raspbian distribution.

Next Up Hooking up the Hardware

Other Things Breadboard - A prototyping board Wires - To connect the Raspberry Pi GPIO pins to the Breadboard. 4.7k resistor

Wiring the sensor to the Raspberry Pi The sensor has 3 pins: 1. With the flat side of the sensor facing you connect the pin on the right to the 3.3v pin on the raspberry PI. 2. Connect the pin on the left to a GND pin on the Raspberry PI. 3. Connect the middle pin to the Pin labeled #4 4. Use a 4.7k resistor to connect the right and middle pins.

Next Up Lessons Learned from writing the first software.

First software attempt The first version of the sensor used the sqlite python module for logging the temperature data. SD-Cards like the ones in the Raspberry Pi can only handle a limited number of writes. Left running, and sd-card failed after about a month.

Lesson learned Take into account the limited lifespan of the sd-card when writing the software.

Switch to Redis for Logging ● Stores data to RAM memory ● Writes to disk/sd-card are configurable ● Can replicate the data to another computer over a network without writing to the sd-card. ● Easy to understand

Next Up Setting Up Setting up the Raspberry Pi with our software.

Setting up the Software Everything this example uses is either part of the Raspbian OS or installable using the python pip tool. $ pip install redislite redis-collections bottle

Next Up Writing the Code Now we have the sensor all wired up now time to write some code to use it.

Data Logger from redislite import StrictRedis from redis_collections import List from time import sleep def read_temp_c(): with open('/sys/bus/w1/devices/28-000006b63824/w1_slave') as device: for line in device: value = line.strip().split()[-1] if value.startswith('t='): return float(value[2:])/1000.0 redis_connection = StrictRedis('/var/lib/temp.rdb') temp_readings = List(redis=redis_connection, key='temp_readings') while True: temp_readings.append(read_temp_c()) print('Temp C:', temp_readings[-1]) sleep(1)

Web Interface from bottle import route, run from redislite import StrictRedis from redis_collections import List redis_connection = StrictRedis('/var/lib/temp.rdb') temp_readings = List(redis=redis_connection, key='temp_readings') @route('/current_temp') def current_temp(): return str(temp_readings[-1]) @route('/average_temp/') @route('/average_temp/') def average_temp(seconds=3600): seconds=int(seconds) return str(sum(temp_readings[-seconds:])/len(temp_readings[-seconds:])) run(host='0.0.0.0', port=8080, debug=True)

Next Up Networking Sensors So lets see how we can run more than one of these

Networked Data Logger from __future__ import print_function from redislite import StrictRedis from redis_collections import List from time import sleep def read_temp_c(): with open('/sys/bus/w1/devices/28-000006b63824/w1_slave') as device: for line in device: value = line.strip().split()[-1] if value.startswith('t='): return float(value[2:])/1000.0 redis_connection = StrictRedis('/var/lib/temp.rdb', serverconfig={'port': '8002', 'requirepass': 'secret'}) temp_readings = List(redis=redis_connection, key='temp_readings') while True: temp_readings.append(read_temp_c()) print('Temp C:', temp_readings[-1]) sleep(1)

Replicated Web Interface from bottle import route, run from redislite import StrictRedis from redis_collections import List redis_connection = StrictRedis('/tmp/temp.rdb', serverconfig={'slaveof': 'notebook.local 8002', 'masterauth': 'secret'}) temp_readings = List(redis=redis_connection, key='temp_readings') @route('/current_temp') def current_temp(): return str(temp_readings[-1]) @route('/average_temp/') @route('/average_temp/') def average_temp(seconds=3600): seconds=int(seconds) readings=list(temp_readings)[-seconds:] return str(sum(readings)/len(readings)) run(host='0.0.0.0', port=8080, debug=True)

Conclusion Internet of things using Python and the Raspberry Pi is actually very easy.

Questions